APPENDIX. 45 



chemical agencies, modified by the action of decomposing vegetation. The 

 accumulation of laterite in any region would then depend on (i)the solubility of the 

 basal rock, (2) the proportion of contained iron, (3) the fertility of the soil formed 

 by its disintegration, and (4) the climate of the region. 



A somewhat similar view is upheld by Mr. Mallet, 1 who compares the Indian 

 laterite with the ferruginous beds associated with the basaltic rocks of N. E. Ireland. 

 The differences between the two are considerable. The Irish rocks are nearly 

 always compact, and the mottled character so commonly present in laterite is not 

 found in them. They consist partly of magnetic oxide. But Mr. Mallet does not 

 look upon these differences as essential. The Irish beds, as suggested by 

 D. Forbes, have probably been formed in much the same way as the bog iron ore 

 of Sweden, and Mr. Mallet supposes that the Indian laterite was also formed in the 

 same way. He agrees with Mr. McGee in attributing the separation of the iron to 

 the action of decomposing vegetation, but believes that the laterite was formed in 

 lakes and not by decomposition in situ. 



Mr. Ball, 2 in his account of Manbhum and Singhbhum, holds that as the 

 laterite accommodates itself to the contour of the ground, it cannot have been formed 

 in lakes. He is inclined to agree with the view that it is a modified volcanic ash, 

 the iron having been concentrated by segregation. 



Dr. King, 3 in his Geology of Travancore, states that there certainly are cases 

 in which the laterite has been formed by decomposition in situ of gneiss, for it is 

 frequently seen to pass gradually downwards into the gneiss. Detrital laterite 

 occurs near the coast. 



The last paper to which it will be necessary to refer is that of Mr. Bose 4 on 

 the Manganiferous Iron and Manganese ores of Jabalpur. He divides the 

 lateritic rocks into three groups: — (1) Lateritised Bijawar rocks. The gradual 

 change of the Bijawar rocks into laterite is well seen near Gosalpur. (2) Lateritic 

 rocks associated with the Gosalpur quartzites. The lateritic rocks alternate 

 with the quartzites. In several pits large blocks of quartzite were found in situ 

 surrounded on all sides by laterite, and there are other evidences that some of this 

 laterite is formed by alteration of the quartzites. (3) Lateritic alluvium. 



From this summary it will be seen that the view taken by an author has 

 generally depended more or less on the area in which his observations were made. 

 Thus most observers on the East Coast have come to the conclusion that laterite is 

 of sedimentary origin. Those also who saw the laterite of Ouilon and the coast of 

 Travancore, look upon it as detrital. In this they are confirmed by Dr. King, 5 

 who, however, believes that the rock further inland has been formed by decom- 

 position in situ. Further up the West Coast, in the Konkan, most writers are 

 agreed that much of the laterite has been formed by decomposition in situ, though 

 at Ratnagiri, where it overlies plant beds, it must be detrital. 



With regard to the laterite of the Deccan and Western Ghats, opinions are 

 more divided. Mr. Foote's views have already been mentioned, and his evidence 

 is very strong. The theory proposed by Dr. Blanford that laterite is re-assorted 

 volcanic detritus, ash, &c, does not account for the fact that laterite is quite as 



1 Rec. G. S. I., XIV. 139. 



2 Mem.G. S. I., XVIII, 122. 



a Rec. G. S. I., XV, 96. 



* Rec, G. S. I., XXII, 220. 



* Rec, G. S. I., XV, 97. 



( 245 ) 



